1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a computer-readable recording medium on which an image processing program for improving the sharpness and quality of an image is recorded.
2. Description of the Related Art
Image output apparatuses of recent years directly process input multi-value image data as is, to increase the number of representable gradations and colors. On the other hand, there are demands that the image output apparatuses have an outline processing function for handling the multi-value image data in order to eliminate the jaggies of diagonal lines of binary image data such as dark color characters and graphics.
Japanese Patent Laid-Open No. 5-138945 discloses an image output apparatus which was developed in order to meet the above-mentioned social demands. The image output apparatus performs interpolation and gradation processing on images that are adapted to the minimum pixel of a printer engine according to the type of image information.
Japanese Patent Laid-Open No. 6-234240 discloses an image forming apparatus developed in order to meet the above-mentioned social demands. The image forming apparatus comprises color pattern generation unit for reproducing a color image through a color processing unit 504, extraction device for extracting a predetermined image signal through a black dot detecting unit 507, image smoothing unit for passing the image signal extracted by the extraction unit through a pulse width modulation unit 503 to smooth the image, and optical scanning unit for scanning a image carrier by using a light beam modulated according to the above-mentioned image signal, as shown in FIG. 11. In FIG. 11, reference number 505 indicates a smoothing unit, reference number 502 indicates a storage unit, reference number 505 indicates a multi-value signal delay unit, reference number 506 indicates a γ (gamma) correction unit, and reference number 508 indicates a frequency divider.
The above-mentioned pulse width modulation unit 503 is configured so as to latch a multi-value image data, MVIDEO, and input it to the negative inputs of comparators 603 and 604, as shown in FIG. 12. The comparators 603, 604 compare an image clock signals, VCLK and ½ VCLK with the latched signal to modulate the pulse width. In FIG. 12, reference number 601 indicates a latch circuit, reference number 602 indicates a digital-to-analog converter, reference number 605 indicates a selector, reference number 606 indicates an OR circuit, and SVIDEO indicates binary image data.
The image output apparatus disclosed in Japanese Patent Laid-Open No. 5-138945 performs the above-mentioned interpolation or gradation processing after a complex data detection process such as area determination.
The image output apparatus disclosed in Japanese Patent Laid-Open No. 6-234240 performs color processing and black pixel binarization at the same time, therefore the black pixels contained in image information, which do not require smoothing process, are also binarized and smoothed. Furthermore, because the binarized image data is modulated by multi-value image data output from the γ correction unit 506 when the pulse width modulation unit 503 applies pulse width modulation to the binarized image data generated by the smoothing processing unit 501, the smoothing processing is not correctly performed.